Stuff becoming easier is how MMOs work. Whether it's lvling, obtaining gear, making gil you name it, it will become easier as time goes by. Mining/Botany were far out of the loop lvling speed wise compared to the other classes, so it's no suprrise that those are the first classes that have their lvl speed increased.

Fast lvlers have the advantage they get somewhere first and can make use of that position, while slow lvlers got the advantage that by the time they get to certain content it's been made easier. Pick whichever one you want, but don't complain afterwards that you'd rather have made a different choice.